A process for recording information known from German Patent Publication DE-OS 38 34 709 uses a print head having a number of printing elements arranged in columns in a principle direction. The print head is moved line by line in a reciprocating manner relative to a recording substrate, its movement being directed perpendicular to a forward feed direction of the recording substrate (serial printer). During this reciprocating movement the print head passes over a plurality of print positions of a print line.
In the known process, a subgroup, which is the same for all print positions of a print line, is formed from a partial number of printing elements. The printing elements of the subgroup are selectively controlled at every print position according to predetermined print data. Accordingly, depending on the print datum of the respective printing element, ink may possibly be applied to the recording substrate. After passing across a print line, the recording substrate is advanced in accordance with the length of the subgroup in the forward feed direction. The print head can then continue to make recordings during the subsequent return movement (bidirectional printing) or only when a new advancing movement of the print head is effected (unidirectional printing).
If the forward feed of the recording substrate in serial printers does not correspond exactly to the respective height of the pattern which is printed line by line, adjacent print lines overlap presenting overlaid inked areas of superimposed lines (dark stripes), or are visibly distant from one another (light stripes). These effects of incorrect line spacing are referred to in the following as line continuation errors.
Such line continuation errors are caused, for example, by manufacturing tolerances in the mechanical feed of the recording substrate. Also, the amount of feed generally varies with the thickness of the recording substrate so that costly adjustment would be required in the case of recording substrates with different thickness.
Further, in a serial printer which works with an ink ribbon, stripes can also be formed when the ink ribbon is used up unevenly (referred to in the following as ink ribbon structure errors). Such stripes can also be brought about by failure of a printing element. The human eye is very sensitive to such linear structures disrupting the visual impression of the recorded information.
In the process known from German Patent Publication DE-OS 38 34 709 light stripes are prevented in that, in addition to the subgroup determined by the partial number of the printing elements, there is at least one printing element adjacent to the subgroup which is acted upon by the same print datum as its neighboring printing element of the subgroup. Accordingly, in the known process the formation of light--particularly noticeable i.e.--stripes between adjacent print lines is prevented within a wide range of tolerances, but at the expense of dark stripes in the region of the line continuation as a result of the deliberate overlapping of adjacent print lines. The effect of ink ribbon structure errors and failures of printing elements is not diminished by this known process.
In International Patent Application WO 90/14957 it is proposed, in order to prevent perception of uneven side edges of a recording pattern, to arrange print lines produced in bidirectional printing in such a way that their individual printing lines are interlaced. However, the problem of line continuation errors, ink ribbon structure errors and errors due to failure of printing elements persists in this known process as well, since errors can also cause horizontal structures in this case.